This invention is generally related to electronic imaging, and more particularly to changing an image field of view and image frame rate in an imaging apparatus.
Modern electronic imaging systems have become an important part of every household and business, from traditional applications such as video cameras and copiers to more modern ones such as the facsimile machine, scanner, medical imaging devices, and more recently, the digital camera. The digital camera has been developed as a portable system that acquires and stores detailed still images in electronic form. The images may be used in a number of different ways such as being displayed in an electronic photo-album or used to embellish graphical computer applications such as letters and greeting cards. The still images may also be shared with friends via modem anywhere in the world within minutes of being taken.
Most purchasers of digital cameras have access to a desktop computer for viewing the still images. Therefore, such purchasers might also enjoy using the digital camera to communicate with another person via videoconferencing or to view images of motion in a scene. Using a digital camera as a video camera or videoconferencing tool, however, presents requirements that may conflict with those for capturing still images. For instance, due to the limited transmission bandwidth between the camera and a host computer used for viewing video images, the transmitted frames of video images must be of a typically lower resolution than still images.
To meet a given image frame rate over a limited transmission bandwidth, one solution is to simply electronically scale the detailed still image frames into lower resolution image frames prior to transmitting them. Alternatively, the detailed image can be xe2x80x9ccroppedxe2x80x9d to a smaller size, and therefore lower resolution image. In this way, the amount of spatial data per image frame is reduced, so that a greater frame rate can be achieved between the digital camera and the host computer.
Electronic scaling and/or cropping of the detailed image, however, does not address another problem posed by videoconferencing, namely that due to close proximity of the object (a person""s face or body) to the digital camera during the video phone or videoconferencing session, a wider field of view is required of the images. The field of view can loosely be thought of as relating to the fraction of the scene included in the transmitted image frame.
Digital cameras typically use an optical system with a fixed effective focal length. Although a detailed still image using such a camera could have an acceptable field of view for distant scenes, electronically scaling the image for video operation does not increase the field of view, while cropping actually decreases the field of view. Therefore, what is needed is a mechanism that allows a digital camera to capture images of close-up scenes having a wider field of view but with lower resolution, in order to increase frame rate for rapid frame rate applications such as video phones and videoconferencing.
The invention in one embodiment is directed at a circuit for processing first sensor signals to yield first digital image data, where the first signals are generated by an image sensor in response to a first image of a scene projected on the sensor. The circuit is further configured to process second sensor signals to yield second digital image data having a lower resolution than the first data. The second signals are also generated by the image sensor but this time in response to a second image projected on the sensor, where the second image has a greater angular field of view but is smaller than the first image.
The circuit may be incorporated into an imaging apparatus such as a digital camera as a different embodiment of the invention. The imaging apparatus includes the image sensor coupled to an optical system, where the optical system has an adjustable effective focal length, such as in a zoom lens, in order to focus light from a scene onto the sensor to create the first and second images. The second image data is obtained through a combination of (1) the optical system being adjusted to project the second image having a wider field of view than the first image on the image sensor, and (2) the circuit processing the second sensor signals which are generated in response to the second image. The first image data is generated while the camera operates in xe2x80x9cstillxe2x80x9d mode to capture detailed images of distant scenes, whereas the second image data results while operating in xe2x80x9cvideoxe2x80x9d mode to capture less detailed but wider angle images of near scenes typically encountered during, for example, videoconferencing.